Abstract
BACKGROUND AND AIMS: Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is a nuclear-encoded chloroplast protein that modifies the conformation of Rubisco, releases inhibitors from active sites, and increases enzymatic activity. It appears to have other functions, e.g. in gibberellin signalling and as a molecular chaperone, which are related to its distribution within the chloroplast. The aim of this research was to resolve uncertainty about the localization of RCA, and to determine whether the distributions of Rubisco and RCA were altered when RCA content was reduced. The monocotyledon, Oryza sativa was used as a model species. METHODS: Gas exchange and Rubisco were measured, and the sub-cellular locations of Rubisco and RCA were determined using immunogold-labelling electron microscopy, in wild-type and antisense rca rice plants. KEY RESULTS: In antisense rca plants, net photosynthetic rate and the initial Rubisco activity decreased much less than RCA content. Immunocytolocalization showed that Rubisco in wild-type and antisense plants was localized in the stroma of chloroplasts. However, the amount of Rubisco in the antisense rca plants was greater than in the wild-type plants. RCA was detected in both the chloroplast stroma and in the thylakoid membranes of wild-type plants. The percentage of RCA labelling in the thylakoid membrane was shown to be substantially decreased, while the fraction in the stroma was increased, by the antisense rca treatment. CONCLUSIONS: From the changes in RCA distribution and alterations in Rubisco activity, RCA in the stroma of the chloroplast probably contributes to the activation of Rubisco, and RCA in thylakoids compensates for the reduction of RCA in the stroma, allowing steady-state photosynthesis to be maintained when RCA is depleted. RCA may also have a second role in protecting membranes against environmental stresses as a chaperone.
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Claims 10
Claim · model-written summary
Antisense rca plants had lower net photosynthetic rate, with a smaller decline than RCA content.
- Taxon
- Rice Leaves
Oryza sativat0 - Treatment
- antisense rcae0
- Gene
- RCAe0
- Outcome
- net photosynthetic ratee0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In antisense rca plants, net photosynthetic rate and the initial Rubisco activity decreased much less than RCA content.”
t0“Rice Leaves”
Claim · model-written summary
Initial Rubisco activity declined less than RCA content in antisense rca plants.
- Taxon
- Rice LeavesOryza sativat0
- Treatment
- antisense rcae0
- Gene
- Rubiscoe0
- Outcome
- initial Rubisco activitye0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In antisense rca plants, net photosynthetic rate and the initial Rubisco activity decreased much less than RCA content.”
t0“Rice Leaves”
Claim · model-written summary
Rubisco was localized in chloroplast stroma in wild-type and antisense plants.
- Taxon
- Rice LeavesOryza sativat0
- Material
- wild-type and antisense plantse0
- Gene
- Rubiscoe0
- Outcome
- localized in the stroma of chloroplastse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Rubisco in wild-type and antisense plants was localized in the stroma of chloroplasts.”
t0“Rice Leaves”
Claim · model-written summary
Antisense rca plants contained more Rubisco than wild-type plants.
- Taxon
- Rice LeavesOryza sativat0
- Treatment
- antisense rcae0
- Gene
- Rubiscoe0
- Outcome
- amount of Rubiscoe0
- Direction
- greatere0
- Comparator
- wild-type plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the amount of Rubisco in the antisense rca plants was greater than in the wild-type plants.”
t0“Rice Leaves”
Claim · model-written summary
RCA occurred in both chloroplast stroma and thylakoid membranes of wild-type plants.
- Taxon
- Rice LeavesOryza sativat0
- Material
- wild-type plantse0
- Gene
- RCAe0
- Outcome
- detected in both the chloroplast stroma and in the thylakoid membranese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“RCA was detected in both the chloroplast stroma and in the thylakoid membranes of wild-type plants.”
t0“Rice Leaves”
Claim · model-written summary
Antisense rca substantially decreased the percentage of RCA labeling in thylakoid membranes.
- Taxon
- Rice LeavesOryza sativat0
- Treatment
- antisense rca treatmente0
- Gene
- RCAe0
- Outcome
- percentage of RCA labelling in the thylakoid membranee0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The percentage of RCA labelling in the thylakoid membrane was shown to be substantially decreased, while the fraction in the stroma was increased, by the antisense rca treatment.”
t0“Rice Leaves”
Claim · model-written summary
Antisense rca increased the stromal fraction of RCA.
- Taxon
- Rice LeavesOryza sativat0
- Treatment
- antisense rca treatmente0
- Outcome
- fraction in the stromae0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the fraction in the stroma was increased, by the antisense rca treatment.”
t0“Rice Leaves”
Claim · model-written summary
The authors infer that stromal RCA contributes to Rubisco activation.
- Taxon
- Rice LeavesOryza sativat0
- Gene
- RCAe0
- Outcome
- activation of Rubiscoe0
- Qualifier
- probablye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“RCA in the stroma of the chloroplast probably contributes to the activation of Rubisco”
t0“Rice Leaves”
Claim · model-written summary
The authors infer that thylakoid RCA compensates for reduced stromal RCA to maintain steady-state photosynthesis.
- Taxon
- Rice LeavesOryza sativat0
- Gene
- RCAe0
- Outcome
- steady-state photosynthesis to be maintainede0
- Qualifier
- when RCA is depletede0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“RCA in thylakoids compensates for the reduction of RCA in the stroma, allowing steady-state photosynthesis to be maintained when RCA is depleted.”
t0“Rice Leaves”
Claim · model-written summary
RCA may protect membranes against environmental stresses as a chaperone.
- Taxon
- Rice LeavesOryza sativat0
- Gene
- RCAe0
- Outcome
- protecting membranes against environmental stressese0
- Qualifier
- as a chaperonee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“RCA may also have a second role in protecting membranes against environmental stresses as a chaperone.”
t0“Rice Leaves”
The same questions in other papers
loss of function · physiology: photosynthesis · Oryza sativa (rice)Positive and negative results
13 papers in the same direction as this paper · 4 in the opposite direction
- positive
- positive
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See all 18 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.